Microsoft Windows up to Server 2019 Reparse Point access control

Summaryinfo

A vulnerability identified as problematic has been detected in Microsoft Windows up to Server 2019. This vulnerability affects unknown code of the component Reparse Point Handler. The manipulation leads to access control. This vulnerability is referenced as CVE-2020-16877. Remote exploitation of the attack is possible. No exploit is available. Applying a patch is the recommended action to fix this issue.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in Microsoft Windows up to Server 2019 (Operating System). This issue affects some unknown functionality of the component Reparse Point Handler. The manipulation with an unknown input leads to a access control vulnerability. Using CWE to declare the problem leads to CWE-284. The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor. Impacted is integrity, and availability. The summary by CVE is:

<p>An elevation of privilege vulnerability exists when Microsoft Windows improperly handles reparse points. An attacker who successfully exploited this vulnerability could overwrite or delete a targeted file that would normally require elevated permissions.</p> <p>To exploit this vulnerability, an attacker would first have to log on to the system. An attacker could then run a specially crafted application that could exploit the vulnerability and overwrite or delete files.</p> <p>The security update addresses the vulnerability by correcting how Windows handles reparse points.</p>

The weakness was published 10/13/2020 as confirmed security guidance (Website). The advisory is shared at portal.msrc.microsoft.com. The identification of this vulnerability is CVE-2020-16877. The exploitation is known to be easy. The attack may be initiated remotely. Neither technical details nor an exploit are publicly available. The price for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 02/24/2026). MITRE ATT&CK project uses the attack technique T1068 for this issue. The advisory points out:

An elevation of privilege vulnerability exists when Microsoft Windows improperly handles reparse points. An attacker who successfully exploited this vulnerability could overwrite or delete a targeted file that would normally require elevated permissions. To exploit this vulnerability, an attacker would first have to log on to the system. An attacker could then run a specially crafted application that could exploit the vulnerability and overwrite or delete files. The security update addresses the vulnerability by correcting how Windows handles reparse points.

It is declared as proof-of-concept.

Applying a patch is able to eliminate this problem. A possible mitigation has been published immediately after the disclosure of the vulnerability.

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Productinfo

Type

• Operating System

Vendor

• Microsoft

Name

• Windows

Version

• 10 1903
• 10 1909
• 10 2004
• Server 1903
• Server 1909
• Server 2004
• Server 2019

License

• commercial

Website

• Vendor: https://www.microsoft.com/
• Product: https://www.microsoft.com/en-us/windows

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